Only offer to verify if a cross-signed device is available (#5433)

* Only offer to verify if a cross-signed device is available

* Fix tests

* use the right exception mapper

* adjust flag name and logic in ChooseSelfVerificationState

* add comment

* switch order of states to match previous logic

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/encryption/EncryptionService.kt

@@ -17,6 +17,7 @@ interface EncryptionService {
     val recoveryStateStateFlow: StateFlow<RecoveryState>
     val enableRecoveryProgressStateFlow: StateFlow<EnableRecoveryProgress>
     val isLastDevice: StateFlow<Boolean>
+    val hasDevicesToVerifyAgainst: StateFlow<Boolean>
 
     suspend fun enableBackups(): Result<Unit>